The present invention relates to a method of manufacturing a dielectric ceramic composition, a multi-layer ceramic capacitor, and other electronic devices containing a dielectric layer.
A multi-layer ceramic capacitor is being broadly used as a compact, large capacity, high reliability electronic device. The number used in each piece of electrical equipment and electronic equipment has also become larger. In recent years, along with the increasing miniaturization and improved performance of equipment, there have been increasingly stronger demands for further reductions in size, increases in capacity, reductions in price, and improvements in reliability in multi-layer ceramic capacitors.
Multi-layer ceramic capacitors are normally produced by stacking and firing a paste for formation of the internal electrodes and a slurry (paste) for formation of the dielectric using the sheet method or printing method etc. Generally Pd or a Pd alloy had been used for the internal electrodes, but Pd is high in price and therefore relatively inexpensive Ni or Ni alloys is now being used. When forming the internal electrodes by Ni or an Ni alloy, firing in the atmosphere ends up causing the electrodes to oxidize. Therefore, in general, after the binder is removed, the electrodes are fired at an oxygen partial pressure lower than the equilibrium oxygen partial pressure of Ni and NiO, then are heat treated to cause reoxidation of the dielectric layer (Japanese Unexamined Patent Publication (Kokai) No. 03-133116 and Japanese Patent No. 2787746).
If firing electrodes in a reducing atmosphere, however, the dielectric layer is reduced and the specific resistance ends up becoming smaller. Therefore, a reduction-resistant dielectric material which is not reduced even if fired in a reducing atmosphere has been proposed (I. Burn et al., xe2x80x9cHigh Resistivity BaTiO3 Ceramics Sintered in COxe2x80x94CO2 Atmospheresxe2x80x9d, J. Mater. Sci., 10, 633 (1975); Y. Sakabe et al., xe2x80x9cHigh-Permittivity Ceramics for Base Metal Monolithic Capacitorsxe2x80x9d, pn., J. Appl. Phys., 20 Suppl. 20-4, 147 (1981)).
A multi-layer ceramic capacitor using these reduction-resistant dielectric materials, however, suffers from the problems of a short high temperature accelerated lifetime of the insulation resistance and a low reliability. Further, there is the problem that the relative permittivity of the dielectric falls along with time. This is particularly remarkable under a DC electric field. If the dielectric layer is made thinner to make the multi-layer ceramic capacitor smaller and larger in capacity, the field intensity applied to the dielectric layer for giving the DC voltage becomes larger. Therefore, the change in the relative permittivity along with time ends up becoming much greater.
In the standard established in the EIA standard and known as xe2x80x9cX7Rxe2x80x9d, however, the rate of change of the capacity is set as within xc2x115% (reference temperature 25xc2x0 C.) between xe2x88x9255xc2x0 C. and 125xc2x0 C. As a dielectric material satisfying the X7R characteristic, a BaTiO3+SrTiO3+MnO based composition shown in for example Japanese Unexamined Patent Publication (Kokai) No. 61-36170 is known. This composition, however, suffers from a large rate of change of the capacity under a DC electric field. For example, if a DC electric field of 50V is applied for 1000 hours at 40xc2x0 C., the rate of change of the capacity ends up becoming from xe2x88x9210% to xe2x88x9230% and the X7R characteristic can no longer be satisfied.
Further, in the standard of the capacity-temperature characteristic known as the B characteristic (EIAJ standard), the rate of change is set to within xc2x110% (reference temperature 20xc2x0 C.) between xe2x88x9225xc2x0 C. to 85xc2x0 C.
Further, in addition, as a reduction-resistant dielectric ceramic composition, mention may be made of the BaTiO3+MnO+MgO disclosed in Japanese Unexamined Patent Publication (Kokai) No. 57-71866, the (Ba1xe2x88x92xSrxO)aTi1xe2x88x92yZryO2+xcex1((1xe2x88x92z)MnO+zCoO)+xcex2((1xe2x88x92t)A2O5+tL2O3)+wSiO2(where, A=Nb, Ta, V; L=Y or a rare earth element) disclosed in Japanese Unexamined Patent Publication (Kokai) No. 61-250905, barium titanate added with Ba2Ca1xe2x88x92aSiO3 disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-83256, etc.
In all of these dielectric ceramic compositions, however, when the thickness of the dielectric layer is for example a super thin one of not more than 4 xcexcm, it is extremely difficult to satisfy all of the characteristics of the capacity-temperature characteristic, the change in capacity under a DC electric field along with time, the accelerated lifetime of the insulation resistance, the drop in the capacity under a DC bias, etc. For example, in the disclosures of Japanese Unexamined Patent Publication (Kokai) No. 61-250905 and Japanese Unexamined Patent Publication (Kokai) No. 2-832, the problems arise of a short accelerated lifetime of the insulation resistance or a large drop in the capacity under a DC bias.
The present invention was made in view of these circumstances and has as its object to provide a method of manufacturing an electronic device containing a dielectric layer such as a multi-layer ceramic capacitor able to satisfy both of the capacity-temperature characteristics of the X7R characteristic (EIA standard) and the B characteristic (EIAJ standard), even when the dielectric layer is superthin, and having a small change in the capacity under a DC electric field along with time and further having a long accelerated lifetime of the insulation resistance and a small drop in capacity under a DC bias. Further, the present invention has as its object to provide a method of manufacturing a dielectric ceramic composition suitable for use as a dielectric layer of an electronic device containing a dielectric layer such as a multi-layer ceramic capacitor having such superior characteristics.
To achieve the above object, the present invention provides a method of manufacturing a dielectric ceramic composition comprising:
a main component expressed by the formula BamTiO2+n, wherein the xe2x80x9cmxe2x80x9d in the formula is 0.995xe2x89xa6mxe2x89xa61.010, xe2x80x9cnxe2x80x9d is 0.995xe2x89xa6nxe2x89xa61.010, and the ratio of Ba and Ti is 0.995xe2x89xa6Ba/Tixe2x89xa61.010,
a second subcomponent including a sintering aid containing silicon oxide as a main component, and other subcomponents,
comprising the steps of:
mixing the main component and at least part of the subcomponents except for the second subcomponent and to prepare a pre-calcination powder,
calcining the pre-calcination powder to prepare a calcined powder, and
mixing at least the second subcomponent in said calcined powder to obtain a dielectric ceramic composition having ratios of the subcomponents to the main component of predetermined molar ratios.
According to a first aspect of the present invention, said second subcomponent has a composition expressed by (Ba,Ca)xSiO2+x (where, x=0.8 to 1.2);
said other subcomponents include at least:
a first subcomponent including at least one type of compound selected from MgO, Cao, BaO, SrO, and Cr2O3 
a third subcomponent including at least one type of compound selected from V2O5, MoO3, and WO3, and
a fourth subcomponent including an oxide of R (where, R is at least one type of element selected from Y, Dy, Tb, Gd, and Ho); and
at least the second subcomponent is mixed in the calcined powder to obtain a dielectric ceramic composition having ratios of the subcomponents to 100 moles of the main component of:
the first subcomponent: 0.1 to 3 moles,
the second subcomponent: 2 to 12 moles,
the third subcomponent: 0.1 to 3 moles, and
the fourth subcomponent: 0.1 to 10.0 moles (where, the number of moles of the fourth subcomponent is the ratio of R by itself).
According to a second aspect of the invention,
said second subcomponent has a composition expressed by (Ba,Ca)xSiO2+x (where, x=0.8 to 1.2);
said other subcomponents include at least:
a first subcomponent including at least one type of compound selected from MgO, CaO, BaO, SrO, and Cr2O3,
a third subcomponent including at least one type of compound selected from V2O5, MoO3, and WO3,
a fourth subcomponent including an oxide of R (where, R is at least one type of element selected from Y, Dy, Tb, Gd, and Ho), and
a fifth subcomponent including Mno; and
at least the second subcomponent is mixed in the calcined powder to obtain a dielectric ceramic composition having ratios of the subcomponents to 100 moles of the main component of:
the first subcomponent: 0.1 to 3 moles,
the second subcomponent: 2 to 12 moles,
the third subcomponent: 0.1 to 3 moles,
the fourth subcomponent: 0.1 to 10.0 moles (where, the number of moles of the fourth subcomponent is the ratio of R by itself), and
the fifth subcomponent: 0.05 to 1.0 mole.
Note that in this specification, the oxides comprising the main component and the subcomponents are expressed by stoichiochemical compositions, but the oxidized state of the oxides may also deviate from the stoichiochemical compositions. The ratios of the subcomponents are found by converting the amounts of the metals contained in the oxides comprising the subcomponents to oxides of the above stoichiochemical compositions. Further, it is possible to use the above oxides and their mixtures and composite oxides as powder materials of the dielectric ceramic composition, but it is also possible to suitably select, mix, and use various compounds changing to the above oxides or composite oxides by firing, for example, carbonates, oxalates, nitrates, hydroxides, and organic metal compounds may be used.
Further, the ratio between Ba and Ca in the second subcomponent may be any ratio. It is also possible to include only one.
In the present invention, the average grain size of the main component is not particularly limited, but preferably is 0.1 to 0.7 xcexcm, more preferably 0.2 to 0.7 xcexcm.
In the present invention, preferably, said pre-calcination powder is prepared and calcined so that the molar ratio of the components contained in the pre-calcination powder becomes a (Ba+metal element of the first subcomponent)/(Ti+metal element of the fourth subcomponent) of less than 1 or a (Ba+metal element of the fourth subcomponent)/(Ti+metal element of the first subcomponent) of more than 1.
In the present invention, preferably when preparing the pre-calcination powder, the first subcomponent is always included in the pre-calcination powder.
In the present invention, the pre-calcination powder including the fourth subcomponent is calcined at a temperature of at least 500xc2x0 C. to less than 1200xc2x0 C., More preferably 600xc2x0 C. to 900xc2x0 C. Further, when the pre-calcination powder does not contain the material of the fourth subcomponent, the calcination temperature is preferably 600 to 1300xc2x0 C., more preferably 900 to 1300xc2x0 C., particularly preferably 1000 to 1200xc2x0 C.
Note that the calcination may be performed a plurality of times.
The calcined powder may have mixed into it at least the second subcomponent. If necessary, it may have mixed in it at least one of the main component, first subcomponent, third subcomponent, fourth subcomponent, and fifth subcomponent and the composition of the finally obtained dielectric ceramic composition may be made the above range.
According to a third aspect of the present invention, there is provided a method of manufacturing a multi-layer ceramic capacitor comprised of an internal electrode comprised of Ni or an Ni alloy and a dielectric layer alternately stacked, the dielectric layer including by molar ratio 100 moles of BaTiO3, 0.1 to 3 moles of at least one type of MgO and CaO, 0.05 to 1.0 mole of MnO, 0.1 to 5 moles of Y2O3, 0.1 to 3 mole of V2O5, and 2 to 12 moles of BaaCa1xe2x88x92aSiO3 (where xe2x80x9caxe2x80x9d is a number of 0 to 1), comprising
pre-mixing and calcining at 900xc2x0 C. to 1300xc2x0 C. BaTiO3 and at least one type of MgO, CaO and a compound changing to MgO or CaO by heat treatment and using at least 70 wt % of the calcined material with respect to the dielectric material as a whole.
According to a fourth aspect of the present invention, there is provided a method of manufacturing a multi-layer ceramic capacitor comprised of an internal electrode comprised of Ni or an Ni alloy and a dielectric layer alternately stacked, the dielectric layer including by molar ratio 100 moles of BaTiO3, 0.1 to 3 moles of at least one type of MgO and CaO, 0.05 to 1.0 mole of MnO, 0.1 to 5 moles of Y2O3, 0.1 to 3 mole of V2O5, and 2 to 12 moles of BaaCa1xe2x88x92aSiO3 (where xe2x80x9caxe2x80x9d is a number of 0 to 1), comprising
pre-mixing and calcining at 900xc2x0 C. to 1300xc2x0 C. BaTiO3 and at least one type of compound selected from MgO, CaO and a compound changing to MgO or CaO by heat treatment, MnO or a compound changing to MnO by heat treatment, Y2O3 or a compound changing to Y2O3 by heat treatment, and V2O5 or a compound changing to V2O5 by heat treatment and using at least 70 wt % of the calcined material with respect to the dielectric material as a whole.
In the third and fourth aspects of the present invention, the average grain size of the BaTiO3 is preferably 0.2 to 0.7 xcexcm. Note that in the third and fourth aspects of the present invention, the number of moles of the Y2O3 is not the number of moles of Y alone, but the number of moles of the Y2O3.
In the method of manufacturing a dielectric ceramic composition of the related art, BamTiO2+n and additives are mixed once to prepare a mixed powder of the dielectric ceramic composition or a dielectric paste. In the method of the related art, however, segregation of the additives (first to fifth subcomponents) etc. occurs in the dielectric ceramic composition after firing and variance of the composition ends up arising between crystals. Due to this segregation, the permittivity and insulation resistance of the dielectric deteriorates.
According to the present invention, by mixing and calcining at least one of the main component, first subcomponent, third subcomponent, fourth subcomponent, and fifth subcomponent, that is, all except the second subcomponent, variance in the composition between crystal particles can be suppressed. As a result, the precipitation of the segregated phases can be suppressed and the size of the segregated phases may be controlled. Therefore, according to the present invention, it is possible to produce a dielectric ceramic composition suitable for use for a multi-layer ceramic capacitor or other electronic device containing a dielectric layer satisfying both of the X7R characteristic and B characteristic and having a small change in capacity under a DC electric field along with time, a long accelerated lifetime of the insulation resistance, a small drop in capacity under a DC electric field, and a superior reliability. This has been first discovered by the present inventors etc.
Further, the dielectric ceramic composition obtained by the method of manufacture according to the present invention can be fired even under a reducing atmosphere since it does not contain elements such as Pb, Bi, and Zn which evaporate and disperse. Therefore, it becomes possible to use Ni or an Ni alloy or another base metal as an internal electrode and possible to reduce the costs.
Further, the dielectric ceramic composition obtained by the method of manufacture according to the present invention satisfies the X7R characteristic and B characteristic, has a small deterioration of the capacity aging characteristic and insulation resistance due to application of the DC electric field, and a superior reliability even if fired under a reducing atmosphere. Therefore, the method of the present invention is promising as an effective technique for suppressing the deterioration of the rate of change of the temperature in the high temperature region along with a reduction in the thickness of the layer of the multi-layer capacitor.
Further, the dielectric ceramic composition obtained by the method of manufacture according to the present invention can provide a product with a small detrimental impact on the environment due to disposal etc. after use since it does not contain Pb, Bi, or another substance.
Further, in the method of manufacture according to the present invention, it is possible to realize a dielectric ceramic composition of a homogeneous structure with little different phases formed by precipitation of additives and possible to improve the permittivity and insulation resistance of the dielectric ceramic composition. Further, in the method of manufacture according to the present invention, it is possible to provide a multi-layer ceramic capacitor having a high reliability since it is possible to prevent structural defects arising incidentally.
Further, it is possible to easily produce a multi-layer ceramic capacitor or other electronic device containing a dielectric layer with a capacity-temperature characteristic satisfying the X7R characteristic and B characteristic since precipitation of different phases can be suppressed without changing the composition of the additives.